Diablo is a census-designated place (CDP) in Contra Costa County, California, United States. The population was 988 at the 2000 census. It is located 2.5 miles (4.0 km) east-northeast of Danville.
According to the United States Census Bureau, the CDP has a total area of 1.0 square miles (2.5 km²), all of it land.
A post office was established at Diablo in 1916.
As of the census of 2000, there were 988 people, 341 households, and 308 families residing in the CDP. The population density was 1,016.6 people per square mile (393.3/km²). There were 348 housing units at an average density of 357.0/sq mi (138.1/km²). The racial makeup of the CDP was 94.64% White, 0.61% Black or African American, 2.94% Asian, 0.61% from other races, and 1.21% from two or more races. 3.54% of the population were Hispanic or Latino of any race.
In terms of real estate prices, Forbes magazine rated Diablo the fourth most expensive ZIP code in the United States.
There were 341 households out of which 37.8% had children under the age of 18 living with them, 85.3% were married couples living together, 3.5% had a female householder with no husband present, and 9.4% were non-families. 8.2% of all households were made up of individuals and 4.7% had someone living alone who was 65 years of age or older. The average household size was 2.90 and the average family size was 3.03.
In the CDP the population was spread out with 26.8% under the age of 18, 3.8% from 18 to 24, 17.1% from 25 to 44, 38.6% from 45 to 64, and 13.7% who were 65 years of age or older. The median age was 46 years. For every 100 females there were 96.0 males. For every 100 females age 18 and over, there were 90.3 males.
The median income for a household in the CDP was $197,904, and the median income for a family was $220,000. Males had a median income of $190,000 versus $62,614 for females. The per capita income for the CDP was $95,419. None of the population or families were below the poverty line.